With the increasing popularity of mobile terminals that have a GPS (Global Positioning System) function in recent years, there is a growing demand for location information services that offer information relating to a user's present locality. In addition, mobile terminals incorporating a terrestrial digital broadcast reception function are also being developed. Against this backdrop, it is easy to envisage the development in the near future of mobile terminals equipped with a GPS-based location information acquisition function, a terrestrial digital broadcast reception function, and an Internet access function using communication. The widespread use of such mobile terminals will make it possible to provide more useful location information services than heretofore.
A known general location information service that has been available for some time is a service whereby location information is reported from a GPS-equipped mobile terminal to a server, information on the present locality of this mobile terminal is retrieved on the server side, and the retrieved results are sent back to the mobile terminal. That is to say, this is a service whereby information on the present locality can be obtained when a terminal user explicitly orders information retrieval.
In contrast to this, there is a method whereby information retrieval is performed at regular intervals when a user moves (changes location), and when there is information desired by the user in the present locality, the existence of information is reported to the user. Here, this method will be referred to as a notification type content distribution service.
A conventional example of a notification type content distribution service is the method shown in Sakata et al, “A Proposed Location-aware Notification Service” (in Japanese), IPSJ-MBL (2000-MBL-15), December 2002.
The notification type service described in the above document employs a “wide-area cache system” as a retrieval system in order to reduce the cost of communication between a terminal and the server. With this wide-area cache system, a terminal performs en bloc caching from a server of location related information of a wider range that the range that is the object of retrieval, and the terminal performs retrieval processing on this cached location related information. In this way, it is possible to reduce the number of times communication is performed between a terminal and a server.
However, with this kind of conventional method, since actual content distributed over a wide range is cached en bloc, a user does not necessarily view the entire cached content. A consequent problem is that there is a high probability of received content being destroyed without being viewed, and there is room for improvement in the efficiency of content distribution.